1. Field of the Invention
The present invention relates to a PCM (pulse code modulated) audio signal recording and/or reproducing apparatus for recording and/or reproducing a PCM audio signal by using a rotary head.
2. Description of the Prior Art
A standaridzation for the so-called 8 mm video tape recorder has been set internationally. With such standardization, as shown in FIG. 1, recording and/or reproducing are carried out by a pair of first and second channel rotary magnetic heads H1 and H2 mounted to a rotary drum RD with an angular spacing of 180.degree. therebetween, and a magnetic tape TP is wrapped around 221.degree. of the peripheral surface of a tape guide drum and then guided. In a 180.degree. interval of the 221.degree., a video signal is recorded and/or reproduced, while a PCM audio signal with a compressed time base is recorded and/or reproduced in the interval of the remaining 36.degree.. Such prior art 8 mm video tape recorder is disclosed, for example, in Machida et al, U.S. Pat. No. 4,551,771.
The azimuths of the head gaps of the first and second channel rotary magnetic heads H1 and H2 are made different from each other by +100. In the vicinity of the second channel rotary magnetic head H2, there is provided an auxiliary rotary magnetic head H3 for a variable speed playback mode which is spaced apart from the second channel rotary magnetic head H2 with a distance corresponding to two horizontal periods on the tape TP. The azimuth of the gap of this auxiliary rotary magnetic head H3 is selected to be the same as that of the gap of the first channel rotary magnetic head H1.
There is further provided an erase rotary magnetic head He with an angle of 90.degree. relative to the first and second channel rotary magnetic heads H1 and H2. The gap width of the erase rotary magnetic head He corresponds to the width of two skewed tracks In FIG. 1, reference letter d designates the rotation direction of the rotary magnetic heads H1, H2, H3 and He. In this case, the auxiliary rotary magnetic head H3 precedes the second channel rotary magnetic head H2. Reference letters g.sub.1, g.sub.2, g.sub.3 and g.sub.e designate head gaps of the first and second channel rotary magnetic heads H1, H2, the auxiliary rotary magnetic head H3 and the erase rotary magnetic head He, respectively.
Referring to FIG. 1, guide pins G1 and G2 are shown to define a tape wrapping angle at which the tape TP is wrapped around the tape guide drum formed of the rotary drum RD and a fixed drum (not shown). The tape TP is transported in a direction t and this direction t is the same as the rotation direction d of the rotary drum RD. The U.S. patent application of Okada et al, Ser. No. 838,626 for such video tape recorder comforming to such standardization as described above was already filed by the assignee of this application on Mar. 11, 1986.
FIG. 2 shows a format of a recording track formed on a tape according to the above mentioned standardization. From the right-hand side at which the rotary head begins to contact with the tape, at the tip end of the track there is provided a tracing start area 21 of 5.degree. of a rotation angle of the rotary head. At the rear portion of the tracing start area 21, over 2.06.degree. (corresponding to 3 horizontal intervals (H) of a video signal), there is provided a clock run-in area 22 which is synchronized with succeeding PCM data. Next to the clock run-in area 22, there is provided a PCM data area 23 over 26.32.degree. for use with an audio signal with a compressed time base. A period or area of 2.06.degree. (3H) next to the PCM data area 23 is assigned as a back margin area 24 for coping with the erroneous displacement of the recording position upon the so-called after-recording mode. Next to the back margin area 24, there is provided a guard area 25 of 2.62.degree. between a video area and PCM data area. This guard area 25 is followed by a video signal area 26 of one field period over 180.degree. and next to this video signal area 26, there is further provided a detaching area 27 of 5.degree..
Accordingly, with this standardization, the video signal of one field period is recorded on and/or reproduced from the video signal area 26, while the audio signal of 1/60 second period corresponding thereto is pulse-code-modulated, corrected for error and the like, time-base, compressed to about 1/6.8 and then recorded on and/or reproduced from the PCM data area 23. This recording track is slantly and sequentially formed in the longitudinal direction of the tape TP, whereby the successive video signal and audio signal can be recorded and/or reproduced.
In the afore-mentioned standardization, if the 180.degree. of the video signal area 26 is divided equally by 5, each divided segment is given 36.degree.. While, if the 26.32.degree. of the PCM data area 23, the 5.degree. of the tracing start area 21, the 2.06.degree. of the back margin area 24 and 2.62.degree. of the guard area 25 are added, they just form a length of 36.degree.. For this reason, it is proposed to contruct an apparatus for the exclusive use for recording and/or reproducing an audio signal by utilizing the apparatus conforming to the standardization as described above. Such special apparatus is disclosed in Morio et al, U.S. Pat. No. 4,542,419.
FIG. 3 shows one example of a format of recording track by such apparatus.
Referring to FIG. 3, the area extending from the tracing start area 21, in which the rotary magnetic head begins to contact with the tape, to the guard area 25 is formed equivalently to that of the above mentioned standardization and this area is assigned as a first segment. From the start of the former video signal portion 26, there are sequentially provided a tracing start area 31, a clock run-in area 32, a data area 33, a back margin area 34 and a guard area 35 and this interval is assigned as a second segment. Further, a similar arrangement to the second segment is repeatedly provided at every 36.degree. of the video signal area 26 and they are assigned as third to sixth segments. Next to the sixth segment, there is provided a detaching area 27 of 5.degree..
As a result, there are provided separate six segments. ,Then, with respect to each of these respective segments, the rotation angular position of the rotary head is controlled for recording and playback. During a time period corresponding to a desired segment (period) of 36.degree., the PCM data is generated and the recording of such data on the tape is carried out. During that time period the reproduced signal is read from the tape so that playback or reproducing is carried out. Thus, it is possible to independently record the PCM audio signal on and/or reproduce it from six separate track channels made of the alignment of segment tracks which are alternately scanned by the rotary heads H1 and H2. When the re-recording is carried out on a tape that was used once, the erase rotary head (so-called flying-erase head) He is used to erase previously recorded data, and during only a time period in which the rotary erase head He contacts with a desired segment, the erase head He is driven to selectively erase the segment of that period so that a re-recording of that segment only can be accomplished.
As described above, the PCM audio signal can be independently recorded on and/or reproduced from each track channel which is divided by 6 in the widthwise direction of the magnetic tape. For example, it becomes possible, by using a tape capable of, for example, 2-hour recording, to record the PCM audio signal for 12 hours which recording time is 6 times the recording time.
While the first channel rotary head H1 scans a first segment of a certain recording track, the second channel rotary head H2 scans a 6th segment of the following recording track, etc.